@main
enum Queue {
    /* Diver Code */
    static func main() {
        var queue: [Int] = []
        queue.append(1)
        queue.append(3)
        queue.append(2)
        queue.append(5)
        queue.append(4)
        print("队列 queue = \(queue)")
        let peek = queue.first!
        print("队首元素 peek = \(peek)")
        let pool = queue.removeFirst()
        print("出队元素 pop = \(pool)，出队后 queue = \(queue)")
        let size = queue.count
        print("队列长度 size = \(size)")
        let isEmpty = queue.isEmpty
        print("队列是否为空 = \(isEmpty)")
    }
}